Osseous cyst-like lesions in the distal phalanx can result in a lameness that varies from mild to severe and may be unresponsive to anti-inflammatory medication. There is no apparent breed or sex predisposition. The cysts are commonly first diagnosed in young horses (1–3 yr old) but may be diagnosed in older horses. It is unknown whether the cysts have a developmental or traumatic origin. They are most commonly located in the subchondral bone either in the extensor process or along the joint surface close to the midline; the cysts may communicate with the distal interphalangeal joint. The lameness may be exacerbated with distal limb flexion, and it usually responds to intra-articular anesthesia of the distal interphalangeal joint if the cysts communicate with the joint. The lameness may respond to palmar digital nerve anesthesia but more commonly requires a more proximal nerve block (eg, abaxial sesamoid) for resolution of the lameness. Diagnosis is confirmed by radiography and/or CT. Differential diagnoses include keratoma, navicular disease, and primary degenerative joint disease of the distal interphalangeal joint. Surgical treatment includes arthroscopic debridement; extracapsular (through the hoof wall) approaches to the cysts have been used in less accessible lesions. Secondary fracture of the extensor process has been reported to occur due to a cyst in that region. Some horses return to performance status, whereas others are used for alternative purposes such as breeding.

Was This Page Helpful?

Also of Interest

Test your
knowledge

In all animals, the motor unit of skeletal muscle consists of the motor neuron, the neuromuscular junction, and muscle fibers. Muscle dysfunction—such as ataxia, paresis, or paralysis—most commonly originates in which of the following locations?

Merck and the Merck Veterinary Manual

Merck & Co., Inc., Kenilworth, NJ, USA is a global healthcare leader working to help the world be well. From developing new therapies that treat and prevent disease to helping people in need, we are committed to improving health and well-being around the world. The Merck Veterinary Manual was first published in 1955 as a service to the community. The legacy of this great resource continues as the Merck Veterinary Manual in the US and Canada and the MSD Manual outside of North America.